Abstract: Eighty-six left- and right-handed male and female adults received demonstrations of the manual actions involved in tying three different knots from either left- or right-handed female instructors. Learning was greatly facilitated by concordance of handedness between teacher and student, Sex of subject had no effect, nor were any interaction effects significant. Therefore, it is conceivable that observation learning of manual skill, which accompanied the hominid evolution of tool-use and tool-making skills, could have provided selective pressure for concordance (the right-bias) in human handedness.